<template>
  <div class="slider" ref="slider">
    <div class="slider-group" ref="sliderGroup">
      <slot></slot>
    </div>
    <div class="dots">
      <div class="dot" v-for="(item,index) in dots" :class="{active: currentPageIndex===index}"></div>
    </div>
  </div>
</template>
<script type="text/ecmascript-6">
import BScroll from 'better-scroll'
import {
  addClass
} from 'common/js/dom'
export default {
  props: {
    loop: {
      type: Boolean,
      default: true
    },
    autoPlay: {
      type: Boolean,
      default: true
    },
    interval: {
      type: Number,
      default: 4000
    }
  },
  data() {
    return {
      dots: [],
      currentPageIndex: 0
    }
  },
  created() {},
  mounted() {
    // 为什么是20ms? 浏览器刷新通常是17ms一次
    setTimeout(() => {
      this._setSliderWidth();
      this._initSlider();
      this._initDots();

      if (this.autoPlay) {
        this._play();
      }
    }, 20);
    window.addEventListener('resize', () => {
      if (!this.slider) {
        return
      }
      this._setSliderWidth(true);
      this.slider.refresh();
    })
  },
  methods: {
    _setSliderWidth(isResize) {
      this.children = this.$refs.sliderGroup.children;

      let width = 0;
      let sliderWidth = this.$refs.slider.clientWidth;
      for (var i = 0; i < this.children.length; i++) {
        let child = this.children[i]
        addClass(child, 'slider-item');
        child.style.width = sliderWidth + 'px';
        width += sliderWidth;
      }
      if (this.loop && !isResize) {
        width += 2 * sliderWidth;
      }
      this.$refs.sliderGroup.style.width = width + 'px';
    },
    _initSlider() {
      this.slider = new BScroll(this.$refs.slider, {
        scrollX: true,
        scrollY: false,
        momentum: false,
        snap: true,
        snapLoop: this.loop,
        snapThreshold: 0.3,
        snapSpeed: 400
          // click: true
      })

      this.slider.on('scrollEnd', () => {
        let pageIndex = this.slider.getCurrentPage().pageX;
        if (this.loop) {
          pageIndex--;
        }
        this.currentPageIndex = pageIndex;

        if (this.autoPlay) {
          clearTimeout(this.timer);
          this._play();
        }
      })
    },
    _initDots() {
      this.dots = this.loop ? new Array(this.children.length - 2) : new Array(this.children.length);
    },
    _play() {
      let pageIndex = ++this.currentPageIndex;
      if (this.loop) {
        pageIndex++;
      }
      this.timer = setTimeout(() => {
        this.slider.goToPage(pageIndex, 0, 400)
      }, this.interval)
    }
  },
  destroyed() {
    clearTimeout(this.timer)
  }
}
</script>
<style lang="scss" scoped>
@import "src/common/scss/variable";
.slider {
  position: relative;
  min-height: 1px;
  .slider-group {
    position: relative;
    overflow: hidden;
    white-space: nowrap;
    .slider-item {
      float: left;
      box-sizing: border-box;
      overflow: hidden;
      text-align: center;
    }
    a {
      display: block;
      width: 100%;
      overflow: hidden;
      text-decoration: none;
    }
    img {
      display: block;
      width: 100%;
    }
  }
  .dots {
    position: absolute;
    right: 0;
    left: 0;
    bottom: 12px;
    text-align: center;
    font-size: 0;
    .dot {
      display: inline-block;
      margin: 0 4px;
      width: 8px;
      height: 8px;
      border-radius: 50%;
      background: $color-text-l;
      &.active {
        width: 20px;
        border-radius: 5px;
        background: $color-text-ll;
      }
    }
  }
}
</style>
